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The use of carbondioxide as ref in the us?

Oh well.

Got a thougth 'bout that a few days ago while I was filling up a half-empty sub critic carbon dioxide system (most common) for a bigger grocery store. Here in sweden the CO2 systems are well used on bigger grocery stores freezers (both DX and as cold carrier), just for it's effiency, together with cold carrier for the refrigerators, and to chill the CO2-Tank. Some systems uses R404A or R407C to chill the CO2 as well.
As reciprociating compressors for CO2 DX were using Bitzer octagon series as they seem to stand for the high pressures.

Yeap. High pressures it is, but not necessary higher pres. than 410A on hot side if you chilling it down below 32degF. Ordinary Seamless copper pipes for ref use., for trans critic which uses higher pressures than sub critic I think there's harder restrictions.

For mostly there's DX on cold side, hot side is often chilled by return cold carrier line or 404A/407C/other way. Just to keep pressure down.

Here in Sweden the CFC:s is completley forbidden since january 1st 2000 (oh well R12 circuits up to 900g is allowed), HCFC:s has a fill-stop since january 1st 2002, and getting completley forbidden january 1st 2015 for circuits with 3 kg filling and above.

Our HFC:s are soon being out-taxed. The goverment (Or was it EU?) want to get rid of the HFC:s as well. They've started with the cars Aircons. Some stuipidness from the EU commission. The car producers aren't allowed to fill a car with R134, if the model is type confirmed after january 2012.

The best with CO2. If you need to empty a circuit just pull the gas out in the free air, low level, just fill it up, no need to find a leak or make a control report for fixed leak or so. But, were tryin to keep the cost down on gas, pretty expensive. We use a leak detector designed especially for CO2. Using it in same way as a regular hfc detector.